The U.S. president has moved fast to boost green jobs and reclaim international leadership on climate change - he now needs to put those promises into action
As U.S. President Joe Biden marks his first 100 days in office Friday, there's no question he has put his country firmly back on course to tackle climate change, analysts say.
But the test for the rest of his first year is whether he can deliver on his new plans and pledges.
After his predecessor, climate change sceptic Donald Trump, halted any move towards a green transition and yanked the United States out of the Paris climate accord, Biden faced a backlog of work and dug into it from his first day in the White House.
He immediately rejoined the flagship Paris Agreement to curb global warming, started planning this month's international leaders' climate summit, and there unveiled a new 2030 target to cut U.S. emissions 50-52% below 2005 levels.
Greg Carlock, manager for climate action and data at the Washington-based World Resources Institute US, told the Thomson Reuters Foundation the new target is "ambitious, achievable and absolutely necessary" to meet the goals of the Paris Agreement.
Some green groups criticised the world's second-biggest emitting country for not taking on what they call a "fair share" of the burden of taming climate change, given its large historical role in belching out climate-heating gases.
But John Podesta, a climate adviser to former President Barack Obama and founder of the Center for American Progress, said the new 2030 U.S. target would help keep the world on track to limit global warming to 1.5 degrees Celsius.
That is the more ambitious goal in the Paris pact and the warming limit scientists say gives the best chance of avoiding devastating surges in hunger, poverty and displacement fuelled by even more extreme weather and sea level rise.
Carlock noted that besides efforts to reclaim international leadership on climate change, Biden had filled his cabinet and advisor positions with "climate champions" who have a strong green track record, such as special climate envoy John Kerry.
Biden also launched a "whole of government" approach to climate change, asking every government body and agency to consider the issue in its decisions and budgeting.
And he issued executive orders and actions aimed at slimming the federal government's carbon footprint, prioritising justice and equity in clean energy investment, and addressing climate-related migration, among many other things.
Now he aims to put big money behind his vision, presenting a $2.3 trillion jobs and infrastructure plan last month in a bid to secure a "once-in-a-generation investment to put the economy on track for a clean energy future", Carlock said.
"In terms of 100 days, it's a complete righting of the ship," the analyst added.
"From the technical and policy side, I think (Biden) is doing what needed to be done to take this issue seriously and put the full weight of the United States behind solving a problem."
Now, U.S. climate experts say, the challenge is to put flesh on the bones of the promises made during the president's first three months and ensure those pledges bring real-world change.
For that, he will need to get his infrastructure package - which Republican lawmakers have already rejected as too large - through Congress, which is likely to prove a bumpy ride.
Democrats, with effective control of the Senate and a slim majority in the House of Representatives, aim to deliver a final bill for the Democratic president to sign into law between July 4 and early September.
Biden is gambling that his spending plans, which are largely popular with American voters, can sway Republicans in Congress to cooperate with the White House.
But a bipartisan group of lawmakers is already working on an alternative that would cost half as much but direct three times more spending to revitalising U.S. roads and bridges.
Senate Republicans also unveiled their own five-year, $568-billion infrastructure proposal last week.
Carlock said Biden's plan would put in place the bricks-and-mortar investments needed to start decarbonising the power sector and expanding electrification of transport and other parts of the economy.
It would also spur efforts to retrofit buildings to use less energy and boost manufacturing of clean technology - all of which would create the "good jobs of the future", Carlock said.
Implementing that plan has international significance too, he added.
The last four years under Trump showed that whatever a country commits to on paper, there are "ways of rolling that back" - and other nations will now want to see the United States is serious about tackling climate change, he said.
The Biden administration needs to turn its climate ambition "into credible, durable action that cannot be so easily reversed by the next president", he added.
Biden's government might also take concrete steps this year to boost climate finance for developing nations, curb vehicle pollution and methane emissions, and make sure federal dollars spent on cities and on industry are climate-smart.
Podesta, Obama's former climate advisor, agreed that what happens in the U.S. legislature between now and November's COP26 U.N. climate summit will be important for galvanising steeper emissions cuts from other major-emitting nations.
"This is now going to be the fulcrum on which the United States will come into the COP with the wind at its back or wind in its face," he told journalists this week.
The White House has claimed it can, if necessary, meet its 2030 emissions reduction goal even without the big new investments Biden has proposed, Podesta said.
Whether that is realistic is "questionable", he added, noting it will be "a lot easier" if Biden can secure additional funding to start deploying clean energy more widely.
Former U.N. climate chief Christiana Figueres said Biden's first 100 days were already having a ripple effect, with share prices in renewable energy firms such as Vestas, Orsted and Acciona soaring after the 2030 U.S. target was unveiled at the Earth Day leaders' summit.
Clean energy assets - such as solar and wind power - are increasingly regarded as a safer investment, which is contributing to a "virtuous circle", she said.
"It is very interesting to see how something that was meant as a political driving force, to bring major countries into the new (climate) effort that we have to engage in... also has direct financial implications," she said.